EFFECT OF Moringa oleifera FLOWER EXTRACT ON LARVAL TRYPSIN AND ACETHYLCHOLINESTERASE ACTIVITIES IN Aedes aegypti

摘要

Aedes aegypti control is crucial to reducing dengue fever. Aedes aegypti larvae have developed resistance to organophosporous insecticides and the use of natural larvicides may help manage larval resistance by increasing elements in insecticide rotation programs. Here, we report on larvicidal activity of Moringa oleifera flower extract against A. aegypti L₁, L₂, L₃, and L₄ as well as the effect of flower extract on gut trypsin and whole-larval acetylcholinesterase from L_4. In addition, the heated flower extract was investigated for larvicidal activity against L₄ and effect on larval gut trypsin. Moringa oleifera flower extract contains a proteinaceous trypsin inhibitor (M. oleifera flower trypsin inhibitor, MoFTI), triterpene (β-amyrin), sterol (β-sitosterol) as well as flavonoids (kaempferol and quercetin). Larvicidal activity was detected against L₂, L₃, and L₄ (LC₅₀ of 1.72%, 1.67%, and 0.92%, respectively). Flower extract inhibited L₄ gut trypsin (MoFTI K_i = 0.6 nM) and did not affect acetylcholinesterase activity. In vivo assay showed that gut trypsin activity from L₄ treated with M. oleifera flower extract decreased over time (0–1,440 min) and was strongly inhibited (98.6%) after 310 min incubation; acetylcholinesterase activity was not affected. Thermal treatment resulted in a loss of trypsin inhibitor and larvicidal activities, supporting the hypothesis that flower extract contains a proteinaceous trypsin inhibitor that may be responsible for the deleterious effects on larval mortality.